Tailoring Coordination Chemistry for Robust Four-Electron Redox in Aqueous Zinc-Iodine Pouch Cells at Low Temperature

ABSTRACTS Aqueous four-electron zinc-iodine (Zn-I2) batteries offer a route to energy-density storage, yet they are severely hampered by sluggish I−/I0/I+ conversion kinetics and electrolyte freezing at subzero temperatures. Here, we report a frost-resistant electrolyte engineering strategy utilizing guanidinium chloride (GuHCl) as an additive, selected based on its unique ion−dipole interactions and coordination capabilities. The GuH+ exerts electrostatic effects, disrupting the tetrahedral hydrogen-bond network of free water. This structural reconfiguration suppresses electrolyte solidification and accelerates Zn2+ transport kinetics at low temperature. Simultaneously, GuH+ exhibits coordination affinity toward both polyiodide intermediates and ICl2− species. This interaction mitigates the polyiodide shuttle effect and inhibits I+ hydrolysis, thereby enhancing the I−/I0/I+ conversion kinetics in the cold. As a result, the formulated electrolyte enables Zn-I2 pouch cells to achieve reversibility, long cycling stability of 1100 cycles, and low operating temperature at –60 °C, achieving a capacity–temperature−lifespan balance that surpasses most reported low-temperature Zn-metal pouch cells.